The Ark of the Covenant is a hierophany, the manifestation of God as king that represents his presence in the tabernacle.
It may be a footstool, and is later actually referred to as the footstool of God; the mercy seat is perhaps the seat upon which a king would sit. Atop the Mercy Seat, or perhaps the cover of the ark, were cherubim, winged creatures also found in the Garden of Eden as well as instructions for what to place in the tabernacle.
Bringing the Ark to Jerusalem
Israel has a persistent enemy at its western border and along the coast. It is the Philistines. The book is bookended with the Philistine problem to emphasize the failure of Saul's reign. Before and after him is the same problem. So what can David do? He can kill Goliath, a heavily armed Philistine. So he is the author's way of suggesting that despite being meek small and younger he can accomplish great military defeats that Saul cannot orchestrate.
He wants Jerusalem to be the capital by innovatively bringing the ark to Jerusalem there. David goes to Nathan who is a prophet, an intermediary through whom David can speak to the deity. Then there is s special point: David does not want to do something radically different from what the Torah wants to be done, As there I'd mention in Deuteronomy of seeking out s place to worship god.
Is the deity mobile? As the Israelites go from nomadic to settled, there is a tension over put ting the deity in just one locale. The author of this text in 2 Samuelson ch 7 then the deity allows David to have a house. We thus get the constitution of sorts for the davidic dynasty. You can't build a house for me David but ill build you a house. The deity is describing to not s physical house or temple but s dynasty, that his blood line will be the legitimate one as rulers. Second Samuel chapter seven becomes wn authorization for the house of David.
Later the house of David and the temple will become wed, the establishment of the Davidic dynasty in Jerusalem and the temple will eventually become one and the same. The temple is a royal chapel, more or less a way if emphasizing that the temple I Jerusalem is intimately connected to kingship. Royalty and temple go hand in hand here, though what about when there is no kingship later in Jerusalem?